JP6284629B2 - Apparatus and method for determining the focal position of a high energy beam - Google Patents

Description

  The invention relates to a device for determining the focal position of a high energy beam, in particular a laser beam, in the beam direction of the high energy beam relative to the workpiece and / or relative to the reference contour of the device. The invention also relates to a method for determining the focal position of a high energy beam, in particular a laser beam, in the beam direction of the high energy beam relative to the workpiece and / or relative to the reference contour of the apparatus. This device is, for example, a machining head, in particular a laser machining head.

  The focal position or focal plane position of the high-energy beam used for workpiece machining is an important parameter for workpiece machining. The position of the focal plane and the focal position in the propagation direction of the high-energy beam depend on the divergence or convergence of the high-energy beam in front of the focusing element, and more precisely the wavelength region of the high-energy beam for the high-energy beam used. Depends on the focal length of the condensing element (when a laser beam of the operating wavelength is used).

The divergence or convergence of the high energy beam is usually well controllable and only minor changes are made according to the basic adjustment. However, when the beam output is large and a CO ₂ laser beam is used, fluctuations in the focal length of the condensing element during workpiece processing are critical. When a lens is used as a condensing element, a temperature gradient in the radial direction is formed by uneven heating or cooling of the lens, and this temperature gradient changes the refractive index n of the lens depending on the coordinates in the radial direction. Result (ie, n = n (r)). Changes in the refractive index in workpiece processing typically result in a reduction in focal length (so-called thermal lens). Accordingly, the actual focal length f _FL of the condenser lens is a function of, among other things, the beam output P _L and the beam shape (eg, beam diameter D _R ), the degree of contamination of the condenser lens, time: f _L = f (P _{L , D R, t, ...)} . Therefore, in order to determine the focal position or focal plane position during workpiece processing, it is usually necessary to consider the actual focal length of the light collecting element.

  In order to determine the focal position of a high energy beam in the beam direction, it is well known to measure, among other things, the beam path or beam line using an appropriate measuring device, and in some cases, the beam output only near the beam waist is detected. Is done. In addition, one notch is provided in the workpiece at each of a plurality of various intervals selected between the light collecting element and the workpiece, and the focal position with respect to the workpiece is estimated based on the width of the notch. Is also possible. However, the means described above typically cannot detect the focal position online, i.e. during workpiece processing.

  From WO 2011/009594, a laser processing head for processing a workpiece using a laser beam is known. This laser processing head focuses a camera with an imaging optical system for monitoring a workpiece processing area, and a laser beam on the workpiece surface or at a predetermined position relative to the workpiece surface. And a condensing lens. Further, in International Publication No. 2011/009594, the focus of the camera image is readjusted when the focusing lens is out of focus, or the focusing optical system is defocused with respect to the workpiece surface or a predetermined position on the workpiece surface. An evaluation unit configured based on the adjustment distance in the optical axis direction of the imaging optical system, which is required for calculating a correction adjustment distance for correcting the image, is disclosed.

  German Offenlegungsschrift 10 201 0017 316 discloses a system comprising a welding device configured to provide a weld bead on a workpiece. The system includes a plurality of cameras configured to generate a corresponding number of images toward the weld bead. The control device creates a three-dimensional image of the weld bead based on the plurality of images, and sets parameters for setting a welding beat based on the three-dimensional image. In addition, here, instead of the plurality of cameras, it is possible to take images from two different transmission directions or viewing directions using a single camera, to perform differential analysis of images, or to generate a stereoscopic image. .

  From German Offenlegungsschrift 102005032946 is known an apparatus for processing an object using a laser beam. This device has a monitoring device for imaging an object and a laser scanning device. This monitoring device may be configured as a stereo microscope having two imaging beam paths and two eyepieces in order to monitor an object in three dimensions in the preparation mode. According to the optical imaging device, it is possible to follow the progress of the processing process during the operation of the laser scanning device with the same eyepiece.

  German Offenlegungsschrift 10 101016519 discloses a method and apparatus for controlling the processing of a workpiece using a high energy machining beam. Here, the machining beam passes through a lens that can move in a direction perpendicular to the optical axis with respect to the deviation of the machining beam incident position with respect to the workpiece. According to one example, a surveillance camera is provided that generates an electronically evaluable image, and the imaging beam path of the camera is focused through the lens at the incident location.

  European Patent No. 2456592 discloses a condensing optical system for condensing a machining laser beam at a predetermined position on the workpiece surface or the workpiece surface, and a beam path for monitoring the workpiece machining area. A laser processing head having a camera equipped with an imaging optical system is disclosed. Here, when the focus of the condensing lens deviates, the sharpness of the camera image is readjusted, and the correction adjustment distance that corrects the defocus of the condensing optical system with respect to the workpiece surface or a predetermined position on the workpiece surface is calculated An evaluation unit configured based on the adjustment distance in the optical axis direction of the imaging optical system, which is necessary for the measurement, is provided.

The problem underlying the present invention is to provide an apparatus and method that can determine the focal position with high reliability during processing of a workpiece using a high energy beam.

Aspects of the invention The object is to provide a device of the type described at the beginning,
A condensing element for condensing the high energy beam on the workpiece;
An image capture device for capturing an area to be monitored on the surface of the workpiece and / or the reference contour using a monitoring beam path extending through the light concentrating element, wherein Configured to form at least one monitoring beam associated with a monitoring direction extending in a non-coaxial direction and at least one of the region to be monitored and / or the reference contour from at least one of the monitoring directions An image capture device including imaging optics for generating one image;
And an evaluation device for determining the focal position of the high energy beam in the beam direction by evaluation of the at least one recorded image.

  The proposed measurement principle for determining the focal position in the beam direction of the high energy beam is the capture of at least one image of the area to be monitored or at least one monitoring direction that is non-coaxial to the high energy beam Or based on the capture of at least one image of a reference contour from at least one viewing angle. That is, a part of the monitoring beam path that penetrates the light condensing element extends at a predetermined angle with respect to the optical axis of the light condensing element. Based on such a monitoring beam, under appropriate evaluation of the recorded image, a change in the focal length of the condensing element or possibly a change in the object spacing, i.e. between the workpiece and the condensing element. Changes in the spacing between are captured and the focal position of the laser beam in the beam direction is determined and corrected as necessary.

  According to an embodiment, the evaluation device is configured to determine a focal position in the beam direction of the high energy beam based on the position of the reference contour in the at least one recorded image. In this case, a reference contour or reference geometry that is statically arranged with respect to the device (which may be formed by the nozzle inner contour of the laser processing nozzle, for example in an apparatus in the form of a laser processing head), Used for focus position determination. This reference contour has a certain distance in the beam direction with respect to a condensing element, for example a condensing lens. Variations in focal length due to, for example, thermal loads on the light concentrator elements lead to lateral shifts of the reference geometry in the recorded image. It is possible to determine the focal position based on the magnitude of the lateral displacement of the position of the reference geometry in the recorded image. It is also possible to estimate the directionality of the focal position deviation from the target focal position based on the directionality of the lateral deviation. For this purpose, the offset or lateral deviation of the reference contour with respect to the reference position, for example under a condensing element without thermal load, is determined. For example, prior to image evaluation, a reference position at the (known) focal length of the light collecting element in a cold state, i.e. without irradiation with a high energy beam, is determined and a memory associated with the evaluation device It may be filed in the device, for example in the form of a reference image or position, for example in the form of a region center, a geometry center or a specific geometric feature, for example a geometric edge form.

  According to a further embodiment, the image capture device is configured to form at least one further monitoring beam associated with a further monitoring direction, the imaging optics being at least two different monitoring directions. At least two images of the region to be monitored and / or the reference contour from the evaluation device, wherein the evaluation device is configured to compare the focus of the high energy beam by comparative evaluation of a plurality of recorded images. It is configured to determine a position.

  The measurement principle proposed for determining the focal position in this embodiment is based on a three-dimensional spacing measurement through the light collection element, i.e. two or more of the areas to be monitored on the workpiece surface. Based on image recording or based on recording two or more images of the area to be monitored in a reference contour provided in the device from two or more different monitoring directions or viewing angles. The imaging optics typically for this purpose typically extend eccentrically of the concentrating element (ie extend without passing through the central axis) and each with respect to the workpiece Imaging beam bundles of imaging or monitoring beam paths on two or more monitoring beams or different areas of one or more detector surfaces extending at different angles. Alternatively to generating two or more images in mutually spaced areas of the detector surface (s), two or more images in the same area of the detector surface are short as described in detail below. It is also possible to capture sequentially and sequentially at time intervals. By comparing and analyzing three or more images, the significance of the comparison and the accuracy of determining the focal position can be increased.

  In order to determine the focal position as accurately as possible, the viewing direction or viewing angle in which the image is recorded is preferably shifted as much as possible from each other. A large difference between the viewing angles is obtained especially when the two images of the surface area to be monitored of the workpiece have passed through two edge areas opposite to each other in the diameter direction of the light collecting element. Typically, one or more condensing lenses or condensing mirrors, in particular off-axis parabolic reflectors are used as the condensing elements.

  When the workpiece is in the focal plane of the condenser lens, the image or image of the area to be monitored of the workpiece from the edge area of the condenser lens is the same. However, when the workpiece is out of the focal plane of the condenser lens, ie above or below, the two images of the area to be monitored on the workpiece surface are laterally offset from each other. Based on the magnitude of the lateral displacement between these two images, it is possible to estimate the spacing or displacement between the workpiece and the focal position or focal plane.

  Correspondingly, it is also possible to estimate the focal position with respect to the device or reference contour or reference geometry based on the lateral spacing between the two images of the reference contour formed in the device. In order to achieve this, the distance between the two images of the reference contour is matched to the (known) focal length of the condensing element in the cold state, i.e. without irradiation with a high energy beam. Changes in the spacing between the two images caused by focal length variations can be accommodated by corresponding changes in the focal position. In this way, it is possible to measure the focal length of the condensing element relative to the apparatus or to determine the focal position without depending on the workpiece.

  In order to determine the lateral shift between multiple images, the spatial correlation of the two images may be performed, for example, by a block matching algorithm or by local frequency analysis to achieve the best matching position. In contrast to the image sharpness adjustment described in WO 2011/009594, stereoscopic measurement is the determination of the amount and direction of focal length deviation (i.e., the direction toward or away from the workpiece). Enable. Thereby, it is possible to quickly control the focal length or the focal position without depending on repetitive tracking control (see below). Obviously, under this stereoscopic imaging, the influence of further optical elements present in the imaging beam path on the basis of changes in focal length or focal position is also taken into account. For example, this also applies to a thermal lens formed by a protective glass that forms the end of the device in the form of a machining head towards the workpiece.

  According to one embodiment, the device comprises an illumination source for illuminating the surface of the workpiece, particularly in the area to be monitored and / or the reference contour. This illumination source can provide illumination under a wavelength of, for example, between 360 nm and 800 nm (VIS), or between about 800 nm and about 1000 nm (NIR). This illumination is used to obtain an image of the contour of the workpiece surface in the area to be monitored or a reference contour formed in the device. This illumination can be carried out coaxially with respect to the high energy beam, ie in the form of vertical illumination. However, this illumination source can also be used to illuminate a predetermined measurement position in which the reference contour or reference geometry is formed. This reference contour may be illuminated, for example, by a directional illumination source or captured by an image capture device. In addition, a cutting nozzle attached to the cutting head for process gas guidance may be used as a reference contour.

  According to one embodiment, the monitoring or imaging beam path of the image capture device that captures the area to be monitored on the workpiece surface has an image capture area that defines a reference contour. In this case, the illumination source illuminates, for example, the workpiece or other surface below the reference contour, and the reference contour or reference geometry forms the boundary of the illumination or image capture area captured by the image capture device.

  According to one embodiment, the evaluation device is configured to determine the focal position of the high energy beam relative to the workpiece by comparatively evaluating images of the (rough) surface of the workpiece. Here, for comparative evaluation or correlation of two images, generally the surface of a plate-like workpiece is not completely smooth, but has a surface structure that varies depending on the location, with roughness (at least on the order of the microscope level). It is used to have. That is, the focal position can be determined based on the lateral distance between the surface structures of a plurality of images recorded from different directions.

  Typically, the area of the workpiece to be monitored includes the area of interaction between the workpiece and the high energy beam. As an alternative or in addition to the three-dimensional correlation of multiple images of the contour of the rough workpiece surface, in some cases the process-specific brightness (thermal radiation, plasma radiation) can be evaluated in a three-dimensional manner. May be used for In either case, it may be used in the form of a structured illumination relative to the illumination of the workpiece, for example an illumination beam focused near the interaction area.

  According to one embodiment, the imaging optical system has at least two imaging optical elements associated with each monitoring direction. These imaging optical elements may be lens elements, for example. These lens elements may be arranged at a predetermined distance from each other. This predetermined distance substantially corresponds to the distance between the two images on the detector surface. Each of the two imaging optical elements here generates a unique imaging or monitoring beam in order to generate an image respectively associated with a corresponding region of the detector surface. The two lens elements are typically off-center, i.e. arranged in the monitoring beam path in a non-coaxial direction relative to the beam path of the high energy beam or to its extension. In this way, two or more beam bundles can be imaged that pass through each edge region of the condenser lens and allow monitoring under two or more different monitoring angles or directions. For example, a spherical lens or an aspherical lens can be used as the imaging optical element. Here, it will be understood that one of the imaging optical elements can be arranged in a coaxial direction with respect to the beam path of the high energy beam, if necessary, as will be described in more detail below.

  According to a preferred improvement, the imaging optical element is formed as a cylindrical lens. In addition to the first cylindrical lens that produces a curvature or imaging action along the first axis, the imaging optical system is generally coupled along a second axis that is perpendicular to the first axis. At least one second cylindrical lens having an image function is included. With these cylindrical lenses arranged in an intersecting manner, the imaging optical system of the present invention can be manufactured on the one hand at low cost, and on the other hand, the available imaging sections can be used effectively.

  According to a preferred improvement, the imaging optical elements are arranged in a lens array or a grid array. A grating array (lenslet or lens array) consisting of a plurality of lens elements, for example a plurality of microlenses, or in the form of two intersecting cylindrical lens arrays, is a local resolution of wavefront aberrations caused by thermally loaded lens elements Can be used to enable automatic detection. With the detection of wavefront aberrations, the beam focusing of the machining beam is optimized using a focusing element, with appropriate beam formation before the focusing element, and / or the coaxial monitoring of the workpiece for process monitoring. May be improved by appropriate modification of the monitoring beam path, possibly under other wavelengths. Modification of the beam shape of the machining beam as well as the monitoring of the workpiece can be realized by deformable mirrors, for example by changing the lens spacing in the beam path, by appropriate adaptation of the blind diameter. . The measurement principle for the determination of wavefront aberration represents the transformation of the Shack-Hartmann sensor, where the local wavefront tilt is measured by the focal shift in the focal plane of the lens array produced by the lenses of the two-dimensional lens array Is done.

  According to another embodiment, the imaging optical system comprises a deflection device having at least two beam deflection regions associated with each monitoring direction. This deflection device can be used as a geometric beam splitter. Thereby, for example, the incident beam is deflected to different regions of the imaging optical element, for example, the lens element. The beam bundle that is deflected by this deflection device and is incident on the region of the lens elements that are opposite to each other in the radial direction is a focal point on which an image of the region to be monitored or the reference contour of the different regions separated from each other is formed by the lens element. Focused on the surface.

  According to another improved configuration, the deflection device comprises at least one deflection prism. In this deflection prism, a plurality of, in particular all, beam deflection regions are formed, which can be configured, for example, as a cut surface or surface region of a prism oriented at a predetermined angle with respect to the beam axis. This deflection prism may be configured as a particularly parallel flat plate and have a central region where no deflection occurs. This beam deflection region or beam deflection surface may be arranged so as to surround the central region. Thereby, a substantially concave or convex geometry of the deflecting prism is produced as a whole. Further, instead of using the deflecting prism, the deflecting device may be configured to be reflective, for example, a plurality of beam deflecting regions in the form of mirror surfaces for deflecting the monitoring beam in various directions corresponding to the respective monitoring directions. You may make it have.

  According to another embodiment, the image capture device that forms at least two monitoring beams associated with each monitoring direction comprises a beam offset device. This beam offset device may be arranged in particular between the two optical elements forming, for example, a telescopic beam, in the focused illumination beam path of the imaging optics. The beam offset device may have two or more blocks made of, for example, a material transparent to the illumination beam, for example made of quartz glass. These blocks are formed as plane parallel blocks or plates in order to form a parallel shift of the incident monitoring beam. These blocks are typically tilted with respect to each other to achieve the incidence of two or more monitoring beams at different regions of the detector plane to produce two or more laterally offset images. Has been placed.

  An image capture device that forms at least two monitoring beams associated with each monitoring direction has a beam splitter. The beam splitter may split the monitoring beam into two or more monitoring beams based on at least one characteristic that varies across the beam cross section. This characteristic may be, for example, a polarization direction according to the power or wavelength of the monitoring beam that varies across the cross section of the monitoring beam path. For the imaging of each monitoring beam on the detector surface, one unique imaging optical element may be provided, but in addition to this, the imaging of this monitoring beam can be performed by, for example, a common condenser lens. It is also possible to use an imaging optical system having a common form.

  According to another embodiment, the image capture device is configured to form at least two monitoring beams associated with the monitoring direction at different times. In this embodiment, two or more images are recorded with a (short) time shift (typically in the range of a few μs or a few ms) depending on the image repetition rate of the image capture device detector or camera. Is done. In this way, two or more images can be generated at one and the same location on the detector surface. That is, spatial separation of the monitoring beam on the detector surface is not necessary in this embodiment. In order to sequentially record images sequentially in time, the monitoring beam path is partially shielded, and typically, different image beam path portions are shielded each time an image is recorded.

  According to another embodiment, the image capture device that forms at least two monitoring beams associated with each monitoring direction has at least one aperture. The aperture is configured or driven to control more than one monitoring beam, especially at different times. For this purpose, the diaphragm may be configured as a shiftable, rotatable or switchable diaphragm, for example. The stop can be used to partially block the monitoring beam path. In that case, different portions of the monitoring beam path can be sequentially shielded sequentially in time by appropriate drive control of the diaphragm. The aperture opening through which the monitoring beam passes typically produces a monitoring beam associated with the monitoring direction. The diaphragm may be configured in the form of an electronic shutter (for example, a liquid crystal display having switchable pixels) or a mechanical shutter (for example, a pinhole movable (for example, rotatable or shiftable) in the diaphragm plane). In order to sequentially generate two or more images from different monitoring directions sequentially in time, different regions of the monitoring beam path may be used so as to be sequentially shielded or opened in time. Here, it is also clear that a further area of the monitoring beam path aperture can be opened and closed for high resolution monitoring of the workpiece monitoring area for process monitoring purposes.

  According to another embodiment, the imaging optics is configured to generate at least three images of the region to be monitored and / or the reference contour from different monitoring directions. As described above, it is usually sufficient to determine the lateral shift along one direction between images recorded from different monitoring directions for the determination of the focal position. However, in some cases, the use of three or more images can increase the usefulness of the comparison and the accuracy of determining the focal position. The generation of at least one further (third, fourth,...) Image can also be used to obtain further information about the concentrating elements, in particular for determining their wavefront aberrations as described above. . Thereby, a change in the focal length of the condensing element or the condensing lens irradiated with a high laser output is detected depending on the position, that is, depending on the radial position of the condensing element with respect to the optical axis. Two or more imaging optics (eg in the form of a lens array) or two or more beam deflection regions are used to generate three or more images of the workpiece surface and / or reference contour and on the detector, eg a camera It is also possible to image on top.

  According to a further embodiment, the device comprises imaging optics that form an image of the area to be monitored on the workpiece surface from the monitoring direction in a direction coaxial to the high energy beam. As noted above, the area to be monitored typically includes an interaction area between the high energy beam and the workpiece. For example, to obtain information about a machining process, such as a welding process or a cutting process, a process-specific illumination of the machining process can be created in the VIS area using coupling optics and / or an area to be monitored. Can be created in the NIR / IR region. The monitoring of the machining process, also referred to as process monitoring, may be additionally performed for a three-dimensional capture of the area to be monitored or the reference contour.

  Typically, the imaging optical element may be a lens element having a larger diameter than the lens element associated with each monitoring direction in order to obtain a high resolution during imaging. This imaging optic is sometimes used for the generation of two or more images recorded from different monitoring directions extending non-coaxial or non-parallel to the direction of propagation of the high energy beam. May be. This is common when the imaging optical system includes a reflecting prism as described above.

  According to an embodiment, the evaluation device compares and evaluates an image recorded in a coaxial direction with respect to the high energy beam and at least one image recorded in a non-coaxial direction with respect to the high energy beam. Is configured to do. Further, based on a comparative analysis of an image recorded in the coaxial direction with respect to the high energy beam and at least one image recorded in a non-coaxial direction with respect to the high energy beam, a focal position of the high energy beam Can also be determined by the method described above.

  According to a further embodiment, the image capture device is configured such that at least one image is recorded by a nozzle opening of a laser processing nozzle for passing a laser beam over the workpiece. In this so-called coaxial monitoring, an image of a region to be monitored of a workpiece is recorded by one or more cameras through a processing nozzle (for example, a laser cutting nozzle) and a condensing element. This device is typically a laser processing head.

  According to one embodiment, the nozzle inner contour of a laser processing nozzle, in particular a laser cutting nozzle, forms a reference contour or reference geometry used for stereoscopic image evaluation. For example, in order to perform a coarse adjustment of the focal position, a lateral distance between two images of a generally circular nozzle inner contour is determined. In this case, since only the interval between two circular boundaries of the workpiece image recorded through the nozzle opening need only be determined, a comparative evaluation of multiple images of the inner contour of the nozzle opening is required. Can be done very quickly. Determining the lateral deviation between multiple images of the workpiece surface, where the workpiece outline or surface geometry must be evaluated, requires more computation time than usual, and for fine adjustment of the focal position Can be used for

  According to one embodiment, the image capture device comprises at least one detector, in particular a camera, having a detector surface on which at least one image is generated. For the capture of multiple images, one and the same detector surface may be used, for example in the form of a camera CCD chip or a CMOS chip. In this case, an image is generated in different partial areas on the detector surface. Particularly preferably in this case, the imaging optics includes a beam telescope for adapting the imaging section to the available detector plane. It will also be apparent that more than one camera may be provided in the image capture device to capture one or more images at each detector plane. In particular, the position of the reference contour is determined by using a simple optical sensor or detector such as a fourth quadrant diode or a line camera instead of a flat camera.

  According to yet another embodiment, the evaluation device is configured to determine a spacing between the reference contour and the workpiece surface by comparative evaluation of recorded images. The distance between the reference contour and the workpiece is the difference between the surface structure on the workpiece, ie the image position on the workpiece surface, and the (same) position in the reference contour in the two recorded images. Can be determined by calculating.

  According to another embodiment, the apparatus further comprises a device for changing a focal position of the high energy beam in the beam direction, and opening the focal position of the high energy beam to a target focal position for the workpiece. An open loop and / or closed loop control device for controlling the loop and / or closed loop. The device for changing the focal position here may be a so-called adaptive mirror, for example, whose surface curvature is controlled as desired in order to change the focal position in the beam direction of the high energy beam. It is possible. Based on the actual focus position determined by the method as described above, the device is driven and controlled such that the focus position is open-loop controlled to the target focus position. It is typically kept constant during the machining process and can be placed, for example, on the workpiece surface side or at a predetermined distance to the workpiece. In this way, the change in the focal length of the condensing element caused by the heat load of the condensing element as described above is compensated. If the device for changing the focal position, i.e. the adjusting element, is in front of the measurement position or in front of the monitoring beam path, control of the focal position to the target focal position is performed. The distance between the reference contour and the workpiece surface is further calculated from the focal position on the workpiece and the calculation of the focal distance of the reference contour in the processing head (for example, laser cutting nozzle) (see above). In some cases, open loop control or closed loop control is performed using an open loop and / or closed loop control device.

  According to a further embodiment, the apparatus comprises: a device for changing a focal position of the imaging optical system in a beam direction of the high energy beam; and the open position of the focal position of the imaging optical system to a target focal position. And / or an open loop and / or closed loop control device for closed loop control. The device or adjusting element for changing the focal position is typically arranged in the monitoring beam path in this case, so that closed-loop control of the focal position of the imaging optics to the target focal position is performed. The target focal position of this imaging optical system is typically present on the workpiece surface to be monitored. Open-loop or closed-loop control to the target focal position can also be performed according to the procedure described in the context of the high energy beam described above.

  The invention also relates to a method of the type as mentioned at the outset, which method comprises the following steps: That is, capturing a region to be monitored on the workpiece surface and / or the reference contour using a monitoring beam path extending through the focusing element; and the region to be monitored and / or the reference Generating at least one image of a contour by forming at least one monitoring beam associated with a monitoring direction extending in a non-coaxial direction relative to the high energy beam; and the beam direction of the high energy beam; Determining the focal position at at least one recorded image.

  According to an advantageous variant embodiment, the focal position of the high energy beam in the beam direction is determined based on the position of a reference contour in the at least one recorded image. As described above, in this case, the focal position is determined based on a lateral shift by comparison with, for example, a reference position of a reference contour in a recorded image.

  According to a further alternative embodiment, at least one associated with a further monitoring direction in order to generate at least two images of the region to be monitored and / or the reference contour from at least two different monitoring directions. Two additional monitoring beams are formed and the focal position of the high energy beam is determined by comparative evaluation of the recorded images. As described above, in the comparative evaluation, a lateral shift between two recorded images or between these structures to be identified is determined, which is relative to the reference contour or the workpiece and the focal position. Represents a measure of relative position.

  The invention also relates to a computer program product comprising code means suitable for carrying out all steps of the above-described method as a computer program on a data processing system. The data processing system may be, for example, an open loop and closed loop control device and / or evaluation device housed in the apparatus as described above, or an external device that is part of a typical processing machine It may be.

  Further advantages of the present invention will become apparent from the following specification and drawings. In addition, the features described above and further described below find use individually or in any combination. It should be noted that the embodiments shown and described below are not to be understood as a limitation meaning, but rather have exemplary character for explaining the present invention.

Schematic diagram of one embodiment of an apparatus for determining the focal position of a laser beam based on two images recorded through a condensing element Plan view of the imaging optics of the apparatus of FIG. Diagram showing two images recorded from different monitoring directions of the area to be monitored of the workpiece at different focal positions of the laser beam Diagram showing two images recorded from different monitoring directions of the area to be monitored of the workpiece at different focal positions of the laser beam Diagram showing two images recorded from different monitoring directions of the area to be monitored of the workpiece at different focal positions of the laser beam Diagram showing the radial beam profile incident on the condenser lens of the device and the resulting radial refractive index profile of the condenser lens The figure which showed the imaging optical system of the apparatus of FIG. 1 a and b provided with the some cylindrical lens The figure which showed the imaging optical system of the apparatus of FIG. 1 a and b provided with the some cylindrical lens The figure which showed the imaging optical system of the apparatus of FIG. 1 a and b provided with the some cylindrical lens Diagram showing the imaging optics of the apparatus of FIGS. 1a and b with a cylindrical lens array Diagram showing the imaging optics of the apparatus of FIGS. 1a and b with a cylindrical lens array Diagram showing the imaging optics of the apparatus of FIGS. 1a and b with a cylindrical lens array Diagram showing the imaging optical system of the apparatus of FIGS. 1a and b with a deflecting prism curved in a substantially convex shape. Diagram showing the imaging optical system of the apparatus of FIGS. 1a and b with a deflecting prism curved in a substantially convex shape. Diagram showing the imaging optical system of the apparatus of FIGS. 1a and b with a deflecting prism curved in a substantially concave shape Diagram showing the imaging optical system of the apparatus of FIGS. 1a and b with a deflecting prism curved in a substantially concave shape Diagram showing the imaging optics of the apparatus of FIGS. 1a and b with a deflection device having two mirror surfaces Diagram showing the imaging optical system of the apparatus of FIGS. 1a and b with a beam displacement device Side and plan views of the imaging optics of the apparatus of FIGS. 1a and b with a rotatable aperture Side and plan views of the imaging optics of the apparatus of FIGS. 1a and b with a rotatable aperture Schematic diagram of one embodiment of an apparatus for determining the focal position of a laser beam based on one image recorded through a condensing element Diagram showing two images of a reference contour recorded from the same monitoring direction at various focal positions of the laser beam Diagram showing two images of a reference contour recorded from the same monitoring direction at various focal positions of the laser beam

  In the following description of the drawings, the same reference numerals are used for the same components or components having the same function.

In FIG. 1 a, an exemplary apparatus 1 for focusing a laser beam 2 onto a workpiece 3, which is not shown in detail but is part of a laser processing machine and configured in the form of a laser processing head. The structure is shown. The laser beam 2 is generated from a CO ₂ laser in the illustrated example, but alternatively, the laser beam 2 may be generated by a solid laser, for example. The laser beam 2 is focused on the workpiece 3 by a condensing element in the form of a condensing lens 4, for example in a laser welding process or a laser cutting process, in order to carry out workpiece processing on the workpiece 3. In the illustrated example, the condensing lens 4 is a lens that condenses the laser beam 2 on the workpiece 3 through the nozzle 5 for laser processing, more specifically, the nozzle opening 5a, that is, in the illustrated example, It is a lens made of zinc selenide that focuses light onto the focal position F of the surface 3a of the workpiece 3. In the case of the laser beam 2 made of a solid laser, for example, a condenser lens 4 made of quartz glass can be used.

  In FIG. 1a, a deflection mirror 6 configured to be partially transmissive is shown. The deflecting mirror 6 transmits the incident laser beam 2 having a wavelength of about 10 μm, and further reflects a monitoring beam for process monitoring (for example, a beam in the visible wavelength region) to a further partially transmissive deflecting mirror 8. . In the case of a laser beam 2 from a solid state laser, the deflection mirror is typically configured to be partially transmissive for wavelengths of about 1 μm. Furthermore, the partially transmissive deflection mirror 8 reflects the monitoring beam to the image capture device 9. The illumination source 10 is used for the coaxial illumination of the workpiece 3 using the illumination beam 11. This illumination beam 11 is transmitted by a further partially transmissive deflection mirror 8 and is deflected onto the workpiece 3 through the nozzle opening 5 a of the laser processing nozzle 5. As an alternative to these partially transmissive deflecting mirrors 6, 8, a scraper mirror or an active device is used to guide the monitoring beam 7 of the image capture device 9 or to guide the illumination beam 11 to the workpiece 3. Hole mirrors (which reflect only the incident beam from the edge region) may be used. In order to enable monitoring, two mirrors provided on the side of the beam path of the laser beam 2 may be used.

  A diode laser or LED may be provided as the illumination source 10. These illumination sources may be arranged coaxially with the laser beam axis 13 as shown in FIG. 1a or may be arranged off the axis. The illumination light source 10 can be arranged, for example, outside (particularly next to) the apparatus 1 and oriented toward the workpiece 3. Alternatively, the illumination source 10 is arranged in the apparatus 1 but can also be oriented on the workpiece 3 non-coaxially with the laser beam 2. In some cases, the device 1 can be operated without the illumination source 10.

  A part of the image capture device 9 may be a geometric high resolution camera 12 arranged behind a further partially transmissive deflection mirror 8 in the monitoring beam path 7. The camera 12 may be a high-speed camera arranged coaxially with the laser beam axis 13 or an extension of the laser beam axis 13 and without depending on the directionality. In the illustrated example, the recording of the image by the camera 12 is performed by the vertical illumination method in the VIS wavelength region. However, the camera 12 is used to record a thermal image of a process-specific illumination or processing process in order to record an NIR / It is also possible to record an image in the IR wavelength region. It is also possible to record multiple images in the UV region to record vertical illumination or process (plasma) beams. If further beam or wavelength components are to be excluded from capture by the camera 12, a filter is placed in front of the camera 12 as in the example shown in FIG. 1a. This filter may be configured, for example, as a narrowband bandpass filter.

  In order to form the images B1, B2 of the area 15 to be monitored of the surface 3a of the workpiece 3 shown in FIGS. 2a-c on the detector surface 12a of the camera 12, the image capture device 9 is imaging optics. In this example, the imaging optical system 14 has two lens elements 16a and 16b disposed in the beam path of the monitoring beam path 7. These lens elements 16a, 16b are arranged in a common plane and only one partial beam or partial bundle of the monitoring beam path 7 forming one monitoring beam 7a, 7b, respectively, is detected by the detector plane 12a of the camera 12. Are formed on two different areas, thereby forming two images B1, B2 spaced apart from each other as shown in FIGS. As can be seen from FIGS. 2 a-c, the regions of the workpiece 3 or images B 1, B 2 imaged from the lens elements 16 a, 16 b, respectively, are defined by the circular inner contour 5 b of the laser processing nozzle 5. In order to adapt the imaging section to the size of the detector surface 12a, the imaging optics 14 comprises a beam telescope having two further lenses 17a, 17b.

  A part of the monitoring beam path 7 (monitoring beams 7a and 7b) formed on the detector surface 12a by the two lenses 16a and 16b, respectively, in the diameter direction of the condenser lens 4 in the X direction of the XYZ coordinate system. The inner contour 5b of the nozzle 5 for laser machining from the two edge areas opposite to the area 15 to be monitored of the workpiece 3 and the different monitoring directions R1, R2 and different monitoring angles with respect to the laser beam axis 13 Is imaged. These two lenses 16a, 16b thereby enable a stereoscopic view of the area 15 to be monitored or the inner contour 5b of the laser processing nozzle 5.

  In FIG. 1 a, the imaging optics 14 has an additional lens 18, which adds a monitoring beam from a central region intersecting the laser beam axis 13 of the condenser lens 4 to the camera 12. Used to image on the detector surface 12a. As can be seen in FIG. 1b, this additional lens 18 has a clearly larger diameter than the two external lenses 16a, 16b used for stereoscopic monitoring. The additional lens 18 is used for process monitoring, more precisely for monitoring the interaction area between the laser beam 2 and the workpiece 3 contained in the area 15 to be monitored. This relatively large diameter of the additional lens 18 produces a relatively large and high pixel count image on the detector surface 12a. This improves the resolution during process monitoring. It should be noted that, unlike FIG. 1a, the additional lens 18 and the accompanying process monitoring can be omitted. In this case, the distance in the X direction between the two lenses 16a and 16b is typically shortened as opposed to FIGS. 1a and b.

  In the following, based on FIGS. 2a-c, in the evaluation device 19 of the apparatus 1, the focal positions F, F ′, F ″ of the laser beam 2 relative to the workpiece 3 are compared between the two recorded images B1, B2. Explain how it is determined by the evaluation.

  In the depiction according to FIG. 2a of the two images B1, B2 produced by the lenses 16a, 16b, the focal position F of the laser beam 2 is present on the surface 3a of the workpiece 3, which in this embodiment is the workpiece processing. Corresponding to the target focal position. The two images B1, B2 capture one segment each corresponding to the area 15 to be monitored of the surface 3a of the plate-like workpiece 3 having the roughness and surface structure illustrated in FIG. 2a. Yes. As can be seen from FIG. 2a, two images of the surface 3a or surface structure of the workpiece 3 recorded through the nozzle openings 5a forming one image capture region are the laser processing nozzles forming one reference contour. Is identical in the area 15 to be monitored, defined by the inner contour 5b of 5, and has in particular no lateral displacement in the X direction. These two images B1, B2 are correlated with the distance between the two lenses 16a, 16b on the detector plane 12a or offset in the X direction by a distance A substantially corresponding thereto.

  In the depiction of the two images B1, B2 shown in FIG. 2b, the focal position F ′ of the laser beam is above the workpiece 3 surface 3a. As can be seen from FIG. 2b, the area 15 to be monitored of the workpiece 3 imaged in the images B1, B2 is not the same, but rather the surface structure to be identified in the images B1, B2 is one each. As indicated by the arrows, they are offset laterally with respect to each other, specifically shifted in the right direction in the first image B1, ie in the positive X direction, whereas in the second image B2 The imaged surface structure is shifted to the left, that is, in the negative X direction. The lateral offset between the imaged surface structures of the workpiece 3 in these two images B1 and B2 depends on the distance from the workpiece 3 to the focal position F ′, and in this case the lateral offset. The deviation in direction increases with increasing spacing between the workpiece 3 and the focal position F ′. Therefore, this deviation represents a measure for the deviation from the target focal position F to the focal position F ′ on the surface 3 a of the workpiece 3. As can be seen in FIG. 2b, in the case of the indicated focal position F ′ on the workpiece 3, the distance A ′ between the two images B1, B2 defined by the inner contour 5b of the laser processing nozzle 5 is also detected. It decreases on the vessel surface 12a. The increase or decrease in the distances A to A ′ between the two images B1 and B2 when the focal position F ′ is shifted in the direction toward the laser processing head 1 depends on the imaging principle used to generate the images B1 and B2. doing.

  In the depiction of the two images B1, B2 shown in Fig. 2c, the focal position F "of the laser beam 2 is below the workpiece 3. As can be seen from this Fig. 2c, it is identified in these images B1, B2. The surface structures of the workpieces 3 are laterally deviated from each other. Specifically, the first image B1 is imaged in the second image B2 in the left direction, that is, in the negative X direction. The surface structure is shifted to the right, i.e. in the positive X direction, as indicated by the arrows, respectively, the workpiece being imaged in the two images B1, B2 defined by the inner contour 5b. The amount of lateral displacement between the surface structures of the piece 3, that is, the offset amount, is a measure of the deviation of the focal position F ″ from the target focal position F of the surface 3 a of the workpiece 3. As can be seen from FIG. 2c, the distance A ″ between the two images B1, B2 defined by the inner contour 5b of the laser processing nozzle 5 also increases on the detector surface 12a.

  It can be seen from a comparison between FIG. 2b and FIG. 2c that the lateral displacement of the two images B1, B2 depends on whether the focal position is above or below the workpiece 3. is there. Therefore, based on the comparative evaluation of the two images B1, B2, where this lateral shift is determined, for example, using a block matching algorithm or by frequency analysis, not only the relative distance of the focal position relative to the workpiece 3 The directionality can also be determined. The same is true for the distances Α to A ′, A to A ″ between the two images B1, B2 on the detector plane 12a, which are the focal positions F to F ′, F To F ″ scale. However, here, it is with respect to the reference contour formed by the nozzle inner contour 5b.

The deviation or deviation of the focal position from the target focal position F on the surface side 3a of the workpiece 3 typically occurs unintentionally during workpiece machining. This is because the refractive index of the condenser lens 4 depends on temperature, as can be seen from FIG. 3 in which the refractive index n of the condenser lens 4 is plotted for each different beam output of the incident laser beam 2. It is. FIG. 3 also shows the beam density (in units of kW / cm ² ), which depends on the location or radius coordinate where it collided with the condenser lens 4 and increases with increasing beam power (in kW). doing. In order to adapt the focal position to the desired focal position F, the thermal load or temperature of the condenser lens 4 during the machining process cannot be predicted, or cannot be predicted sufficiently accurately. Is advantageous for controlling the target focal position F to a desired typical constant value during the machining process.

  For the control of the focal positions F to F ′, F to F ″ to the target focal position, the laser processing head has an open-loop or closed-loop control device 20 connected in signal manner with the evaluation device 19. This open loop / closed loop control device 20 is used for open loop or closed loop control of all laser processing processes, and in the case of this embodiment, a further adaptive deflection mirror provided in the beam path of the laser beam 2. 21, more precisely its curvature acts on an optical surface 21a which can be adjusted in a manner known per se, and the curvature of the adaptive deflection mirror 21 is the focal position F in the beam propagation direction 13 of the laser beam 2. To F ′ and F to F ″. This curvature is set and adjusted using the open loop / closed loop control device 20 as follows. That is, the setting is adjusted so that the deviation due to the heat of the focal positions F ′ and F ″ from the target focal position is just compensated. In the example described here, this means the following. That is, the adaptive deflection mirror until the structures identified in the two images B1, B2 enter the situation shown in Fig. 2a, i.e. have no laterally offset spacing from each other. Means acting on 21.

  It should be understood that the target focal position F does not necessarily have to be the workpiece 3 surface 3a, and the target focal position F can be arranged away from the workpiece 3 surface 3a. In this case, the open loop / closed loop control device 20 is used to control the predetermined lateral spacing between the structures to be identified in the two images B1, B2 corresponding to the desired target focal position. Additionally or alternatively, the focus positions F to F ′ and F to F ″ can be controlled based on the distances A to A ′ and A to A ″ between the two images B1 and B2. In this case, the distances A to A ′ and A to A ″ are controlled to a desired distance A. The desired distance A is set to a target focal position or a target focal distance of the condenser lens 4 with respect to the laser processing head 1. In particular, the focal positions F to F ′ and F to F ″ are roughly adjusted using the distances A to A ′ and Α to A ″. The distances A to A ′ and Α Through A ″ and a comparison between the lateral displacement between the surface structures to be identified in the two images B1, B2, the laser processing nozzle 5, the workpiece 3 or the workpiece 3 surface 3a, The interval D between is determined. Specifically, in order to determine the distance D, the difference between the distance between the same surface structures in the two images B1 and B2 with respect to the edge formed by the reference contour 5b of each image B1 and B2 Is determined (X direction). This difference is associated with an interval D to the workpiece 3 based on a known functional relationship that is obtained or calculated by, for example, test measurement. Also, instead of determining the lateral displacement between the surface structures to be identified in the plurality of images B1, B2, as described above, other features of the workpiece 3 are also used to determine the lateral displacement. Please understand that it is available. For example, in some cases (thermal) images, such as process specific lighting, may also be considered for image evaluation by the evaluation device 19.

  The open loop / closed loop control device 20 can also be used for controlling the focal position of the imaging optical system 14. For this purpose, the open loop / closed loop control device 20 is for shifting the lenses 17a, 17b in the beam direction 13 of the laser beam 2, more precisely for changing the relative distance between the lenses 17a, 17b. Of the device 32. For the sake of simplicity, the same reference numerals F, F ′, and F ″ as the focal position of the laser beam 2 are given to the focal position of the imaging optical system 14. By controlling F ′, F ″, it is ensured that the surface 3a of the workpiece 3 is located within their depth of field, so that the workpiece 3 surface 3a is sharp on the detector surface 12a. Imaged. In order to control the focal positions F, F ′, F ″ to the target focal position on the workpiece 3, the distances A to Α ′, A to A ″ between the two images B1, B2 are determined by test measurements or It is controlled to the calculated target interval.

  As can be seen from FIGS. 4a to 4c, the imaging optical system 14 has an imaging action only in the X direction, not in the Y direction, instead of the spherical lenses associated with the monitoring directions R1 and R2. The cylindrical lenses 16a and 16b may be used. In this case, the additional central lens is also configured as a cylindrical lens 18a. This lens also produces an optical effect only in the X direction. A further cylindrical lens 18b oriented in the Y direction is also used for image formation in the Y direction. Effective use of the cross section available on the detector surface 12a is achieved by the intersecting cylindrical lenses 16a, b, 18a to 18b.

  The imaging optics 14 shown in FIGS. 5a-c also has a plurality of intersecting first and second cylindrical lenses 22, 23, which are 5 × 5 = on the detector plane 12a. Arranged as a grid array 24 to provide 25 pixel counts. The lattice-like array 24 composed of a plurality of lens elements 22 and 23 can be used to detect the wavefront aberration caused by the heat loaded condenser lens 4 with a predetermined local resolution. Based on this wavefront aberration, the beam condensing using the condensing lens 4 is carried out by a suitable beam shaper connected to the front side of the condensing lens 4, which is known per se for beam shaping that will not be described in detail here. Optimized using optical elements. Alternatively or additionally, the coaxial monitoring of the workpiece 3 for process monitoring is improved by appropriate modifications. For example, the monitoring beam path 7 can be adapted by adapting the aperture and / or adapting the distance between the imaging optics and / or by optionally adjustable mirrors.

  An alternative embodiment of the imaging optics 14 comprising an imaging lens 25 and a beam deflection device in the form of a deflection prism 26 is shown in FIGS. 6a, b. The deflection prism 26 comprises four wedge-shaped sections having flat surfaces 26a-d that are angled with respect to the monitoring beam or its beam axis and are arranged to surround a central flat region 27. The first two flat surfaces 26a and 26b are used as a beam deflection region for deflecting the incident monitor beam in the X direction, whereby the monitor beam is in a non-perpendicular direction with respect to the center plane of the imaging lens 25. The first and second images B1 and B2 incident on the imaging lens and spaced apart from each other along the X axis are formed on the detector surface 12a.

  Correspondingly, the third flat surface 26c and the fourth flat surface 26d are beams for forming the third and fourth images B3 and B4 spaced apart from each other along the Y-axis direction on the detector surface 12a. Used as a deflection region. The central flat region 27 that does not deflect the monitoring beam is used to form an image B on the detector surface 12a that is centrally located in the beam path of the monitoring beam. This image can be used for process monitoring as described above. The formation of the four images B1, B2, B3, B4 (these images are compared with each other in pairs) makes it possible to obtain further information about the condenser lens 4, especially wavefront aberrations or two directions ( Suggestions for different heat loads of X to Y) can be obtained. If necessary, comparative evaluation of all three or four images B1, B2, B3, and B4 is performed in order to increase the significance of the correlation and the accuracy in determining the focal positions F, F ′, and F ″. Can also be performed in the evaluation device 19.

  In the embodiment shown in FIGS. 6a and 6b, the shape of the deflecting prism is substantially convex as a whole. The deflection prism 26 shown in FIGS. 7a and b differs from the deflection prism shown in FIGS. 6a and b only in the following respects, ie only in that it has a substantially concave shape. is there. As a result, the correspondence relationship between the images B1 and B2 with respect to the partial beams 7a and 7b of the monitoring beam 7 is reversed, which corresponds to the correspondence relationship shown in FIG. The correspondence relationship between the partial beams of the monitoring beam 7 or the images B1, B2 to B3, and B4 of the beam bundle can be considered when identifying the direction of change of the focal positions F, F ′, and F ″. is there.

  Yet another embodiment of imaging optics with a beam deflection device 26 is shown in FIG. 8a. The beam deflection device 26 here is configured in the form of two mirrors having beam deflection regions in the form of flat mirror surfaces 26a, 26b. Since the two mirror surfaces 26a and 26b are inclined with respect to each other, the incident monitoring beam 7 is reflected in different directions and is in the form of two monitoring beams 7a and 7b associated with the monitoring directions R1 and R2. , Incident at different positions on the detector surface 12a, where the first and second images B1, B2 are formed.

  Yet another means for forming two (or more) images B1, B2 is shown in FIG. 8b. There, two blocks (parallel plane plates) 28a and 28b made of quartz glass are arranged in the region of the monitoring beam path focused on the rear side of the lens 17, and they have two parallel end faces. And is used as a beam offset device. The collected monitoring beams are angled and incident on the beam incident sides of the respective blocks 28a and 28b, are shifted in parallel at the same angle, and are emitted again from the opposite light emitting side. . Based on the large refractive index in the medium having a high optical density of the blocks 28a and 28b, the monitoring beam is perpendicular to the entrance surface or the exit surface in the quartz glass material at a small angle with respect to the normal direction. Propagated to. A part of the monitoring beam incident on each block 28a, 28b forms a monitoring beam 7a, 7b corresponding to each monitoring direction R1, R2, respectively, and these two monitoring beams 7a, 7b are respectively Based on the beam offset, it is shifted laterally and enters the detector surface 12a, where it forms two images B1, B2 that are laterally shifted from each other.

  In the example shown in FIG. 8b, the monitoring beams 7a and 7b intersect as in the example shown in FIG. 6b. This is because the normal directions of the mutually inclined blocks 28a and 28b (perpendicular to the beam incident surface or beam exit surface) intersect in the beam path behind the blocks 28a and 28b. Here, as long as the blocks 28a and 28b are inclined in opposite directions, that is, when their normal directions intersect in the beam path in front of the lens 17, the monitoring beams 7a and 7b are shown in FIG. 7b. It should be understood that it can be propagated as well.

  By comparative evaluation of the two images, the focal position F, F ′, F ″ of the laser beam 2 can be determined using the evaluation device 19 in the manner described above. The same is true for FIGS. The image forming optical system 14 described with reference to FIGS. 7a and 7b and the images B to B1 to B4 recorded using the image forming optical system are naturally applicable, and also in the example described above. In order to shield a part of the monitoring beam 7 which should not reach the detector plane 12a in the beam path of the monitoring beam 7 or is unnecessary for the formation of the two monitoring beams 7a, 7b, It should be understood that more than one (fixed) aperture may be provided.

  Two (or more) monitoring beams 7a based on at least one characteristic that varies across the beam cross section for the formation of two monitoring beams 7a, 7b associated with each monitoring direction R1, R2. , 7b may be used. A beam splitter may be used. The beam splitter may be configured to transmit or reflect the beam component of the monitoring beam path 7 based on, for example, the wavelength, polarization, or output of the monitoring beam. For example, in this beam splitter, the high-power monitoring beam 7b coming from the center of the monitoring beam path 7 may be transmitted, and the low-power monitoring beam 7a coming from the edge region of the monitoring beam path 7 may be reflected.

  FIGS. 9a, b show further means for forming two monitoring beams 7a, 7b associated with each monitoring direction R1, R2, which means that the monitoring beams 7a, 7b are sequentially timed. It differs from the above-described means in that it is formed continuously. As shown in FIGS. 9a and 9b, for this purpose, the imaging optical system 14 is provided with a stop 31, which is supported so as to be rotatable about the rotation axis B. Therefore, when it rotates, the position of the diaphragm opening 31 arranged eccentrically moves around the rotation axis B in an arch shape. The portion of the monitoring beam path 7 that exits through the aperture 31a forms the monitoring beams 7a and 7b. By arranging the stop 31 in the beam path condensed using the lens 17 of the imaging optical system 14, the monitoring beams 7a and 7b are opposed to each other in the monitoring beam path 7, for example, in the diameter direction. Images are formed at the same location on the detector plane 12a sequentially from different areas in time. A plurality of images recorded one after the other by the camera 12 can be comparatively evaluated for determining the focal positions F, F ′, F ″ of the laser beam 2 using the evaluation device 19 as described above. It is.

  Here, instead of the mechanically adjustable diaphragm 31, an electrically adjustable diaphragm, for example in the form of an LCD array in which individual pixels or groups of pixels are electronically turned on and off to produce a shielding effect. It should be understood that can also be used. Also, the mechanical aperture 31 is different from the example shown in FIGS. 9a and 9b, and is moved or shifted laterally with respect to the monitoring beam path 7, for example, in the XY plane, so that different parts of the monitoring beam path 7 are obtained. Can be shielded from light sequentially in time or opened for monitoring. The diaphragm 31 may be realized in the form of one or a plurality of components that can be opened and closed in order to realize the formation of images that are sequentially continuous in time. It may be provided.

  FIG. 10 shows that only one image B1 of the region 15 to be monitored by the camera 12 or the inner contour 5b of the laser processing nozzle 5 forming the reference contour is recorded. A further embodiment of the device 1 in the form of a laser processing head for focusing the laser beam 2 on the workpiece 3 is shown, which is substantially different from the device 1 described above. For this purpose, the (unique) monitoring beam 7 a is formed by the image capture device 9 using the stop 31. This monitoring beam 7a is used to form an image B1 on the detector plane 12a as described above with reference to FIG. 1, and if necessary, a higher resolution image from the monitoring direction R to a high energy beam. 2 is formed by using an imaging optical system 14, which is formed on the detector surface 12 a of the camera 12 in the illustrated example. Two lenses 17a and 17b are provided in a telescopic device for adapting the beam cross section.

  As can also be seen from FIGS. 11 a and b, which show the image B 1, more precisely a predetermined section of the detector surface 12 a, under different focal positions F and F ′ of the laser beam 2, the focal position F , F ′ change, the position of the inner contour 5b forming the reference contour of the laser processing nozzle 5 also changes in the image B1 or on the detector surface 12a.

  In the depiction shown in FIG. 11a, the focal position F of the laser beam 2 is on the surface 3a of the workpiece 3, which corresponds to the target focal position in this example. In the depiction shown in FIG. 11b, the focal position F ′ of the laser beam 2 is above the surface 3a of the workpiece 3 and the position P ′ of the inner contour 5b is the position P shown in FIG. Is shifted laterally (in the negative Y direction). The amount of lateral deviation between these positions P and P ′ in the recorded image B1 depends on the distance from the workpiece 3 to the focal position F ′. This lateral displacement increases with increasing distance between the workpiece 3 and the focal position F ′, so that the deviation is a focal position F ′ from the target focal position F on the surface 3 a of the workpiece 3. Represents a measure for the deviation of. This lateral displacement can be determined, for example, using a correlation between the recorded image B1 and a reference image recorded under the desired target focal position F. Alternatively, the lateral displacement can be determined as follows. That is, it can be determined by determining a characteristic position, such as a geometric center of gravity, or a specific geometric characteristic, such as an object edge, in the recorded image and the reference image. The positional deviation between the characteristic positions in the two images can be determined by comparison and corresponds to a lateral deviation.

  When the focal position F ′ is shifted in the direction of the laser processing head 1, whether the inner contour 5b of the laser processing nozzle 5 in the recorded image B1 is shifted in the positive direction or in the negative Y direction. Whether it is performed depends on the imaging principle used for forming the image B1. The correspondence between the direction of lateral displacement of the inner contour 5b and the direction of shift of the focal position F is unambiguous for a given imaging principle and is therefore based on the direction of lateral displacement. The shift direction of the focal position F can be estimated.

  As shown in FIG. 10, the diaphragm 31 may be configured to be shiftable, and a signal technology connection is formed with the evaluation device 19 and / or the open / closed loop control device 20 for the control of this shift. May be. According to the shift of the diaphragm 31, it is possible to set and adjust a partial region through which the monitoring beam 7a of the condenser lens 4 is transmitted. Thereby, it is possible to deflect the monitoring direction R1 or the monitoring angle, which has proved advantageous for certain applications.

  Even in the case of the apparatus 1 shown in FIG. 10, in order to control the focal positions F to F ′ to the target focal position in the beam propagation direction 13 of the laser beam 2, an open loop / closed loop control device 20 is used. It is possible to act on a further optical element provided in the beam path of the laser beam 2 that causes beam shaping and focus adjustment, in this case the compliant deflection mirror 21, more precisely on its optical surface 21a. . It is also possible to act on other optical elements capable of beam shaping and focus adjustment, for example on lenses with variable focal lengths (eg liquid lenses) or on lenses that can be shifted to a predetermined position in the beam path. Based on the lateral displacement of the inner contour 5b or from the shift amount of the lenses 17a to 17b necessary for focusing correction of the imaging optical system 14 or control of the focal position, the focal positions F and F of the laser beam 2 are obtained. The shift of ', F "can be estimated and this can be controlled and corrected in the laser beam 2.

  The open loop / closed loop control device 20 acts on the shift device 32 for shifting the lenses 17a and 17b in the beam direction 13 of the laser beam 2 as described in connection with FIG. It is also possible to use it for controlling the focal position. In this way it is ensured that the surface 3a of the workpiece 3 is always clearly imaged on the detector surface 12a.

  In summary, as in the method described above, the focal positions F, F ′, F ″ of the laser beam 2 are determined during workpiece processing and are corrected if necessary. The target focal position F is determined by the workpiece. 3 If it is on the upper surface 3a, under a corresponding control of this focal position, it is guaranteed that the workpiece 3 is located in the focal plane of the condenser lens 4. Besides improving the process quality, An image B recorded through the center of the surface 3a of the workpiece 3 (which is used for process monitoring) is also “clear” by the condenser lens 4 under corresponding control of the focal position of the imaging optical system 14. In other words, imaging without defocusing, which improves the process monitoring concerned.

Claims (29)

The focal position (F, F ′, F) of the high energy beam (2) in the beam direction (13) of the high energy beam (2) relative to the reference contour (5b) of the workpiece (3) and / or the device (1). ″) A device (1) for determining,
A condensing element (4) for condensing the high energy beam (2) on the workpiece (3);
A region (15) to be monitored on the surface (3a) and / or the reference contour (5b) of the workpiece (3) using a monitoring beam path (7) extending through the condensing element (4). an image capture device for capturing (9), at an angle to the optical axis of the high energy beam (2) extend in the non-collinear direction relative to and the condensing element (4) Configured to form at least one monitoring beam (7a) associated with a monitoring direction (R1) of the extending monitoring beam path (7) and from at least one of the monitoring directions (R1) An image capture device (9) comprising an imaging optics (14) for generating at least one image (B1) of the area to be monitored (15) and / or the reference contour (5b);
An evaluation device (19) for determining the focal position (F, F ′, F ″) of the high energy beam (2) in the beam direction (13) by evaluation of at least one recorded image (B1); A device (1) characterized by comprising:   The evaluation device (19) determines the focal position (F, F ′, F ″) in the beam direction (13) of the high energy beam (2) as the reference contour in the at least one recorded image (B1). The device (1) according to claim 1, wherein the device (1) is configured to determine based on the position (P, P ') of (5b). The image capture device (9) is configured to form at least one further monitoring beam (7b) associated with a further monitoring direction (R2; R);
The imaging optics (14) comprises at least two images (B1, B2) of the region (15) to be monitored and / or the reference contour (5b) from at least two different monitoring directions (R1, R2); B3, B4) are generated,
The evaluation device (19) determines the focal position (F, F ′, F ″) of the high energy beam (2) by comparative evaluation of a plurality of recorded images (B1, B2; B3, B4). The device (1) according to claim 1, wherein the device (1) is configured as follows.   The device (1) illuminates the workpiece (3) surface (3a), in particular the region to be monitored (15) and / or illuminates the reference contour (5b). The device (1) according to any one of claims 1 to 3, comprising:   The monitoring beam path (7) of the image capture device (9) that captures the area (15) to be monitored on the workpiece (3) surface (3a) is image capture defined by the reference contour (5b). The device (1) according to any one of claims 1 to 4, comprising a region (5a).   The evaluation device (19) is adapted to detect the focal position (F, F ′, F ″) of the high energy beam (2) relative to the workpiece (3) in the area (15) to be monitored. (3) The device (1) according to any one of claims 3 to 5, configured to be determined by comparative evaluation of a plurality of images (B1, B2; B3, B4) of the surface (3a).   The imaging optical system (14) has at least two imaging optical elements (16a, 16b, 22) associated with each monitoring direction (R1, R2). The device (1) according to claim 1.   8. The device (1) according to claim 7, wherein the imaging optical element (16a, 16b, 22) is configured as a cylindrical lens.   9. The device (1) according to claim 7 or 8, wherein the imaging optical element (22) forms a lens array (24).   The imaging optical system (14) includes a deflection device (26) having at least two beam deflection regions (26a, 26b; 26c, 26d) associated with each monitoring direction (R1, R2,...). 10. The device (1) according to any one of claims 3 to 9, comprising a device.   The apparatus (1) according to claim 10, wherein the deflection device (26) comprises at least one polarizing prism.   The image capture device (9) has beam offset devices (28a, 28b) that form at least two monitoring beams (7a, 7b) associated with each monitoring direction (R1, R2; R1, R). 12. The device (1) according to any one of claims 3 to 11, wherein:   The image capture device (9) is configured to form at least two monitoring beams (7a, 7b) associated with each monitoring direction (R1, R2; R1, R) at different times. Item 13. The apparatus (1) according to any one of Items 3 to 12.   The image capture device (9) has at least one stop (31) forming at least two monitoring beams (7a, 7b) associated with each monitoring direction (R1, R2; R1, R). Device (1) according to any one of claims 3 to 13.   The imaging optical system (14) comprises at least three images (B1, B2) of the region (15) to be monitored and / or the reference contour (5b) from different monitoring directions (R1, R2,...). A device (1) according to any one of claims 3 to 14, configured to generate B3, B4).   The imaging optical system (14) provides an image (B) of the region (15) to be monitored on the surface (3a) of the workpiece (3) from the monitoring direction (R) with respect to the high energy beam (2). 16. The device (1) according to any one of the preceding claims, comprising an imaging optical element (18) formed in a coaxial direction.   The evaluation device (19) comprises an image (B) recorded in a coaxial direction with respect to the high energy beam (2) and at least one recorded in a non-coaxial direction with respect to the high energy beam (2). 17. The device (1) according to claim 16, wherein the device (1) is configured to compare and evaluate images (B1-B4). The image capture device (9) has at least one image (B1) by means of a nozzle opening (5a) of a laser processing nozzle (5) for passing the high energy beam (2) over the workpiece (3). Device (1) according to any one of the preceding claims, wherein the device (1) is configured to record -B4, B).   19. The device (1) according to claim 18, wherein a nozzle inner contour (5b) of the laser processing nozzle (5) forms the reference contour. Wherein the image capture device (9) has at least one image (B1 to B4, B) comprises at least one detector having a detector surface (12a) which is generated, any one of claims 1 19 1 A device (1) according to paragraph.   The evaluation device (19) determines the distance (D) between the reference contour (5a) and the workpiece (3) surface (3a) by comparative evaluation of the recorded images (B1 to B4, B). 21. Apparatus (1) according to any one of claims 3 to 20, configured to determine.   The apparatus (1) further comprises a device (21) for changing a focal position (F, F ′, F ″) of the high energy beam (2) in the beam direction (13), and the high energy beam (2). 23. An open loop and / or closed loop control device (20) for controlling the focus position (F ′, F ″) of the target to a target focus position (F) in an open loop and / or closed loop. Device (1) according to any one of the preceding claims.   The device (1) further comprises a device (32) for changing the focal position (F, F ′, F ″) of the imaging optical system (14) in the beam direction (13) of the high energy beam (2). An open-loop and / or closed-loop control device (20) for controlling the focal position (F ′, F ″) of the imaging optical system (14) to a target focal position (F) by open-loop and / or closed-loop control. 23. The device (1) according to any one of the preceding claims, comprising: 24. The apparatus (1) according to any of the preceding claims, wherein the high energy beam (2) is a laser beam. Said high energy beam for the reference contour (5b) and / or the workpiece (3) of the device (1) comprising a condensing element (4) for condensing the high energy beam (2) on the workpiece (3). in the beam direction (13) of (2), the high-energy focal position of the beam (2) (F, F ', F ") a method of determining a
Using the monitoring beam path (7) extending through the condensing element (4), the area (15) to be monitored on the workpiece (3) surface (3a) and / or the reference contour (5b) Step to capture,
Wherein at least one image region to be monitored (15) and / or the reference contour (5b) of (B1 to B4), and extending in non-collinear direction relative to the high energy beam (2) and said condenser Generating by forming at least one monitoring beam (7a) associated with the monitoring direction (R1) of the monitoring beam path ( 7) extending at a predetermined angle with respect to the optical axis of the element (4) When,
Determining the focal position (F, F ′, F ″) of the high energy beam (2) in the beam direction (13) by evaluation of at least one recorded image (B1). A method characterized by that. The focal position (F, F ′, F ″) in the beam direction (13) of the high energy beam (2) is taken as the position (P) of the reference contour (5b) in the at least one recorded image (B1). is determined based on P '), 26. the method of claim 25. In order to generate at least two images (B1 to B4) of the region to be monitored (15) and / or the reference contour (5b) from at least two different monitoring directions (R1, R2), further monitoring directions (R2 Forming at least one further monitoring beam (7b) associated with R);
26. The method according to claim 25 , wherein the focal position (F, F ', F ") of the high energy beam (2) is determined by comparative evaluation of a plurality of recorded images (B1, B2; B3, B4). . 28. Method according to any one of claims 25 to 27, wherein the high energy beam (2) is a laser beam. 29. A computer program comprising code means for carrying out all steps of the method according to any one of claims 25 to 28 as a computer program on a data processing system .

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